Mortality rates from acute renal failure have changed little since 1960, with little progress made in the underlying mechanism(s) for injury or repair. We and others have proposed that there are molecular pathways activated by a variety of renal stresses that result in the syndrome's phenotype. For example, we have found that the gene for p21, a cyclin-dependent kinase inhibitor, is activated to high levels in all types of renal failure and that expression of this gene is protective, both after cisplatin treatment and ischemia-reperfusion. We hypothesized that p21 acts as a cell cycle inhibitor after its induction and that this is the mechanism of its participation and protective effect after acute renal failure. Understanding other pathways and the interrelationships between these pathways is essential before a rational treatment of this syndrome can be approached. Many of these pathways will be dependent on activation and repression of gene transcription, which will be reflected in the change of abundance of mRNAs in the kidney after injury. For this project, we will quantify mRNA profiles in kidneys from untreated mice and compare these profiles with those obtained in kidneys after injury. Inasmuch as we have found that severity of the renal failure phenotype is affected by the presence of p21, we will also compare mRNA profiles from kidneys of injured mice of wild-type genotype and of an isogenic population lacking the p21 gene. Comparison of these two genotypes will establish which genes could contribute either to the increased severity of renal failure seen in p21 (-/-) mice or the lesser damage seen in p21 (+/+) mice. The mRNA profiles obtained from these mice could also reveal genes important for acute renal failure development in general. These profiles will first be approximately by the Serial Analysis of Gene Expression (SAGE) protocol in which the detailed analysis of thousands of transcripts can be assayed and quantified. The SAGE analyses will also provide information about the mRNA coding potential of the untreated and injured kidney. Data from the SAGE analysis will be used to design arrays of genes to be assayed by DNA microarray. The microarray will be used to establish mRNA profiles as well as to reveal pathways affected by acute renal failure.